Photochemical machining of brass with cupric chloride etchants

Abstract:

Photochemical machining is a non-conventional machining
process which employs photoresist and chemical etching
techniques. Brass which contains 60-80% copper and 20-40%-
zinc, is the most commonly etched copper alloy in the UK. It
is used to produce precision parts as well as decorative
items.
In this study, the most widely üsed''brass (BS CZ108, ISO
CuZn37) is etched with cupric chloride. The effects of etchant
concentration, temperature and hydrochloric acid additions on
the etch rate, undercut, etch factors and surface roughness
are determined. In comparison to cupric chloride, ferric
chloride and alkaline etchants were examined.
As an extension to this study, the regeneration of used cupric
chloride and recovery of zinc were examined. This
investigation was needed because the dissolved brass in the
cupric chloride affected the etch rate and surface quality of
the etched brass. Therefore the etchant had to be either
replaced with fresh etchant and the spent etchant disposed of,
or regenerated and the dissolved metal content recovered. The
regeneration/recovery process provided an economical solution
to environmental considerations.
Electrodialysis was used to recover zinc and regenerate cupric
chloride, and the effect of various parameters (i. e. current
density, temperature, catholyte solutions) were examined and
a comparison of costs between electrodialysis and chlorine
regeneration was undertaken.
It was noticed that the electrodialysis produced etchant and
catholyte wastes. In order to eliminate any waste cupric
chloride or catholyte, a further investigation using
cementation was undertaken. It was noted that the cementation
would successfully decrease disposal of excess solutions.